The correct answer is: B. Rough and sticky.
Pollen grains are the male reproductive cells of flowering plants. They are produced in the anthers of the stamen, and are transferred to the stigma of the pistil during pollination.
Insect-pollinated flowers have evolved to attract insects with bright colors, sweet nectar, and sometimes even fragrances. The pollen grains of these flowers are often rough and sticky, which helps them to adhere to the bodies of insects. This ensures that the pollen grains will be transferred to other flowers when the insects visit them in search of food.
Smooth and dry pollen grains are more likely to be blown away by the wind, and are therefore less likely to be transferred to other flowers. Large pollen grains are also less likely to be transferred by insects, as they are more difficult for the insects to carry.
Therefore, the correct answer is: B. Rough and sticky.